The present invention relates to the manufacture of footwear. More specifically this invention relates to the moulding of a sole onto the formed upper of an item of footwear such as a shoe or boot.
Many boots and shoes have an upper formed from a flexible sheet material such as imitation leather or real leather, with a base of the upper mounted on a sole moulded from a polymer plastic or rubber material. The use of synthetic materials in the manufacture of soles for boots and shoes is already well established. PVC, polyurethane, EVA and thermoplastic rubber have all been used to fulfil this purpose. These synthetic materials have suitable functional properties and are aesthetically pleasing as well as being comfortable. Rubber, however, is particularly sought after because of its durability, its resistance to hydrolysis and bacterial attack and its thermal resistance.
During the production process the upper is typically formed around a forming last in a first manufacturing step and then the sole is injection moulded onto a base (i.e. insole) of the upper in a second manufacturing step. The forming last provides a template for the three-dimensional size and shape of the upper. Accordingly, the first step involves mainly shaping and stitching operations. As there is generally no heating involved in this step the last can be made from a variety of materials. Wood and metal have traditional been used, and more recently plastic. Plastic is particularly preferred in lasts today because it is easy to form into the desired shape and is also relatively inexpensive.
The second manufacturing step of the production process involves the injection moulding of the sole onto the base of the upper. As mentioned above, several synthetic materials have been known to be used for the sole. Rubber, however, is seen as being particularly attractive and so-called twin density rubber soles are particularly desirable because they provide a tough out-sole and a resilient mid-sole. Twin density rubber soles therefore provide a durable wear surface at the outsole while maintaining cushioned comfort for the wearer with the resilient mid-sole. Expanded vulcanised rubber in the mid-sole contains cavities or cells (either open or closed) which give the mid-sole its desired level of resilience.
The moulding of rubber soles is an endothermic process and it is therefore necessary to supply generous amounts of heat to the mould. That is, the parts of a mould for a rubber sole must be heated to the appropriate. moulding temperature as the sole is being formed. Because of this necessity to supply heat to the mould, the production process for such rubber-soled footwear has up to now required labour-intensive transfer of the formed upper from the forming last to an injection moulding assembly at which the second manufacturing step could take place. That is, after the first step during which the upper is formed by shaping and stitching on the forming last, the upper is physically transferred from the forming last to a second heated last at the moulding assembly.
This intermediate step of transferring the upper from the forming last to the injection moulding assembly, however, has the disadvantage that it is very labour intensive and can easily add 25% to the manufacturing cost for a pair of shoes. A further disadvantage is that mistakes can occur when placing a lasted shoe on the injection moulding assembly. That is, pre-roughened and/or pre-cemented uppers may be incorrectly placed or aligned, potentially causing a problem with the bonding of the sole to the upper. Not only may this create an unsatisfactory product but it may also delay production while the problem is rectified.
It would therefore be highly desirable to provide a means of integrating the production process steps of forming the upper on the last and moulding the sole onto the upper. This would clearly streamline the production process and reduce the production costs.
According to an aspect of the present invention there is provided a method of making an item of footwear such as a shoe or a boot, including the steps of:
forming an upper for the item of footwear on a forming last, the forming last including a body having the general shape of a foot around which the upper of the footwear item is to be formed, the body having a base corresponding to a sole of the foot shape; and
moulding a rubber sole onto the formed upper while it is still mounted on the forming last, the forming last being heated before and/or during the moulding step,
wherein the step of heating the forming last includes heating the base of the last body, whilst substantially preventing the heating of parts of the body other than the base.
Thus, the upper remains mounted on a single last for the entire process, including for the moulding and vulcanisation of the rubber sole on the upper.
As already mentioned, the moulding of rubber is an endothermic process. Therefore, in a preferred form of the present invention the method includes the step of heating the forming last before and/or during the step of moulding the rubber sole onto the formed upper. The forming last typically includes a body mimicking the general shape of a foot, around which body the upper of the item of footwear is formed. Furthermore, the body typically has a base corresponding to a sole of the foot shape. In a preferred form of the invention the step of heating the forming last includes heating the base of the last body.
Desirably, the step of heating the forming last before and/or during the moulding step is by means of a heating device located within the body.
In a preferred form of the present invention the step of moulding the rubber sole includes;
placing the last with the upper thereon adjacent a mould assembly having a plurality of mould parts;
arranging the mould parts adjacent the base of the last and the upper thereon to define a mould cavity for the rubber sole;
injecting rubber into the cavity; and
applying heat and pressure to the rubber in the cavity to form the sole in adherence with the upper.
The heat may be applied to the rubber in the cavity by the step of heating the last as well as by heating the plurality of mould parts which define the mould cavity for the rubber sole. Naturally, the moulding of the rubber sole includes this application of heat and pressure to the rubber mixture in order to vulcanise the rubber. The step of moulding the sole may also include a two-step moulding process for producing a twin density rubber sole including a relatively compact rubber out-sole and an expanded rubber mid-sole.
It is to be appreciated that the present invention also extends to an item of footwear made in accordance with the method described above.
According to another aspect of the present invention there is provided an apparatus for making an item of footwear such as a shoe or a boot, including:
a forming last including a body mimicking the general shape of a foot around which an upper of the item of footwear is to be formed, the body having a base corresponding to a sole of the foot shape; and
means for moulding a rubber sole onto a formed upper while it is still mounted on the forming last;
the apparatus including means for heating the base of the body of the forming last, and including means for substantially preventing the heating of parts of the body other than the base.
Thus, with the apparatus of the invention it is not necessary to take the shoe or boot upper off the last on which it is formed before the rubber sole can be moulded onto the upper. Rather, the apparatus has means for supplying necessary heat to the forming last to efficaciously mould the rubber sole.
In a preferred form of the invention the means for heating the base of the last body is located within the last. Preferably the base of the last body includes a metallic portion such as one or more metal plate member defining an outer surface of the base to which heat is transmissible from the heating means. The heating means may include one or more electrically activated heating element located inside the last adjacent an inner side of the plate member(s).
In a preferred form of the invention the means for moulding the rubber sole includes:
a mould assembly having a plurality of mould parts to be arranged adjacent the base of the last body, and the upper located thereon, to define a mould cavity for the rubber sole; and
an injector for injecting a rubber mixture into the mould cavity.
The mould parts preferably comprise two side parts, a top part formed by the base of the last and a bottom part which is moveable to compress the rubber during the moulding process. As the injection moulding and vulcanisation of the rubber requires substantial heat, the mould assembly also includes means for heating the side parts and the bottom part of the mould assembly. Typically, these mould parts are heated by electric heating elements embedded therein with those mould parts desirably being formed of metal.
In a preferred form of the invention the apparatus also includes a dummy last in addition to the forming last(s) by means of which a compact out-sole may be formed for a two-density rubber sole. Advantageously, the apparatus of the invention also includes a support which is moveable relative to the moulding means, the forming last and the dummy last being mounted on the support spaced apart from each other.
According to a further aspect of the present invention there is provided a last for making an item of footwear such as a shoe or a boot, including a body mimicking the general shape of a foot around which an upper of the item of footwear is to be formed, the body having a base corresponding to a sole of the foot shape and the last further including means for heating the base of the last body, and means for substantially preventing the heating of parts of the body other than the base.
In a preferred form of the invention the means for heating the base of the last body is located within the last and is preferably in the form of one or more electric heating element. The base of the last body may include a metallic portion such as a plate member to which heat is transmissible from the heating means. At least one electrically activated heating element may be located inside the last adjacent an inner surface of the plate member(s). The plate members desirably extend across the base of the last body.
Preferably, the means for substantially preventing the heating of parts of the body other than the base comprising insulation means between the base and the rest of the body.
In a preferred form of the invention the last body includes a recess or cavity for receiving and housing one or more electrically activated heating element adjacent the plate member(s). The body of the last is preferably formed predominantly from a plastic such as polyethylene. The plate member is preferably formed of a material having good thermal conductivity, eg a metal such as aluminium or steel.
The insulation means serve to insulate parts of the body other than the base, such as the non-metallic parts of the body (in the case of a plastic body, for example) from heat generated by the heating element(s).
Furthermore, in a preferred form of the invention the last body comprises two distinct portions; namely, a heel portion and a toe portion. The heel portion and the toe portion are separable from one another to facilitate removal of an item of footwear from the last after the sole has been moulded.
The above and further features and advantages of the present invention will be more fully appreciated from the following detailed description of preferred embodiments of the invention with reference to the accompanying drawings.